This invention relates to a seismic energy land source for seismic surveying of the earth, and more particularly, to an improved method and apparatus for reducing the stretch of the elastomeric diaphragm of seismic land sources.
Mobile seismic land sources have been constructed in a compact form having the tank in the form of an inverted dome with a displaceable diaphragm covering the bottom of the dome thereby enclosing an incompressible liquid such as water therein. The tank includes an airgun for abruptly releasing pressurized gas into the liquid for generating seismic impulses which are transmitted by a metal plate which is positioned between the diaphragm and the earth so that upon the firing of the airgun and the abrupt release of high pressure gas into the liquid, the flexible diaphragm will suddenly thrust down on the metal plate or pan to displace a portion of the earth beneath the pan thereby transmitting seismic impulses into the earth. One such seismic land source of this type is shown and described in U.S. Pat. No. 4,108,271 which may be referred to for further information with respect to this type of land source.
Although such land sources have proven extremely valuable and are rugged and mobile, the diaphragms of such sources are subject to considerable wear and tear as they are repeatedly subjected to considerable amounts of stretch from the volume of compressed air which is released into the bell or tank each time an airgun is fired thereby bulging or stretching the diaphragm on each such firing. This repetitive and continual bulging and stretching of the diaphragm eventually causes the diaphragm to rupture thereby producing considerable downtime while the diaphragm is replaced and the tank refilled with liquid.